Orbital misalignment of the super-Earth π Men c with the spin of its star

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Planet-planet scattering events can leave an observable trace of a planet's migration history in the form of orbital misalignment with respect to the the stellar spin axis, which is measurable from spectroscopic timeseries taken during transit. We present high-resolution spectroscopic transits observed with ESPRESSO of the close-in super-Earth π Men c. The system also contains an outer giant planet on a wide, eccentric orbit, recently found to be inclined with respect to the inner planetary orbit. These characteristics are reminiscent of past dynamical interactions. We successfully retrieve the planet-occulted light during transit and find evidence that the orbit of π Men c is moderately misaligned with the stellar spin axis with λ = -24.º0± 4.º1 (ψ = 26.º9+5.º8,-4.º7). This is consistent with the super-Earth π Men c having followed a high-eccentricity migration followed by tidal circularisation, and hints that super-Earths can form at large distances from their star. We also detect clear signatures of solar-like oscillations within our ESPRESSO radial velocity timeseries, where we reach a radial velocity precision of ∼20 cm s-1. We model the oscillations using Gaussian processes and retrieve a frequency of maximum oscillation, νmax = 2771+65 -60 μHz. These oscillations makes it challenging to detect the Rossiter-McLaughlin effect using traditional methods. We are, however, successful using the reloaded Rossiter-McLaughlin approach. Finally, in an appendix we also present updated physical parameters and ephemerides for π Men c from a Gaussian process transit analysis of the full TESS Cycle 1 data.

Bibliographic note

20 pages, 11 figures. Published in MNRAS


Original languageEnglish
Pages (from-to)2893–2911
JournalMonthly Notices of the Royal Astronomical Society
Issue number2
Early online date29 Jan 2021
Publication statusPublished - Apr 2021


  • astro-ph.EP, astro-ph.SR